Some of the medicinal components orally administered cause harmful side effects such as nausea and vomiting, when they are adsorbed through stomach to thus cause an abrupt increase of the blood concentration thereof. Accordingly, there have been proposed various kinds of sustained release pharmaceutical preparations to be orally administered in order to prevent any abrupt increase of the blood concentration of the medicinal components thereof (See Patent Documents 1 to 4 specified below).
However, the methods disclosed in Patent Documents 1 to 3 for preparing such sustained release pharmaceutical preparations to be orally administered are quite complicated, which accordingly make the preparation of such sustained release pharmaceutical preparations quite difficult. In addition, the method for the production of the pharmaceutical preparation proposed in the Patent Document 4 is rather simple as compared with the methods for the production of other pharmaceutical preparations, but the former has a problem in that it is difficult to ensure the uniformity of the content of medicinal components in the pharmaceutical preparation and this accordingly makes the practice of the method difficult.
Patent Document 1: JP-A-9-020663
Patent Document 2: JP-A-9-169645
Patent Document 3: JP-A-9-315969
Patent Document 4: JP-A-10-053524